In existing server systems, the power supply (PS) is sized for full system configuration running power virus software. This results in larger power supply size/wattage rating and higher system cost. In high density systems it significantly limits the available board space and system configurations. At the same time, in real applications system utilization remains at about 20-25% level, and the power supply is loaded to a small portion of its power rating. For redundant power supply configurations, where at least two power supplies share common load, average (typical) PS load additionally drops by a factor of two.
A power specification for a computer system, PMAX, usually defines maximum power capability of the power supply in the system. In the process of determining a value of PMAX, system designers usually consider the worst-case configuration of a system. Thus, PMAX for a system represents power consumption when the system is fully populated with hardware. The determination of PMAX also assumes that the system is configured with the most power hungry components capable of being used in that configuration, and that the system is running software that causes it to consume maximum power.
The present methods for determining PMAX, suffer from various disadvantages. First, most systems are populated with less hardware components than their capacity. Second, in the vast majority of cases not all the components used are the most power hungry. For example, many systems may be using slower processors that usually consume less power, and the CPU utilization is infrequently being used to 100% capacity. On average, most of the systems consume power far lower than PMAX, and hence could function adequately with a smaller power supply.
FIG. 1 comprises a histogram of real system CPU utilization in a datacenter over extended period of time (1 week) and clearly illustrates this point. Because of the low utilization rate and recent trend in idle power reduction, system power supplies are oversized, operate at low power levels and therefore have comparatively low efficiency and low power factor. This opens the opportunity for significant power supply size and cost reduction, without affecting system performance, and for improvement system performance-per-watt score.